I have also seen online a diagram of an installation which shows a vented collar where the flue goes through the ceiling into the loft but other examples don't do this and just use a normal collar. Which is correct? I thought a vent collar would allow any fire to spread into the ceiling space.
If you're going to box the twin wall flue in, then you need a couple of inches space around it, and then a vented collar to allow an residual heat to escape, but if it escapes into the loft, then I think you'd need to a roof vent to stop any potential build up of heat up there. This is one for Building control, as not many people handle things this way.
Will the twin wall flue be in just one piece inside the false chimney, as you'd need to have access to any joints to be able to test for leakage
Not sure of the diameter, though perhaps later I'll get a tape measure and find out, just for the Hell of it.
I should know more tomorrow because a HETAS engineer is coming to do a survey for the fitting of a woodburning stove. I assume they'll line it, though I do know someone who was told that because his ex council house had a "well built flue", he wouldn't need a liner prior to the fitting of a woodburner.
In my case I'd rather have one than not, because I believe clay pot liners are prone to cracking.
Sorry about hijacking the thread - thought it was long dead but relevant so would resurrect it but agree it is becoming confusing so thank you Doggit for your help and l'll STFU now!
I assume they'll line it, though I do know someone who was told that because his ex council house had a "well built flue", he wouldn't need a liner prior to the fitting of a woodburner.
A liner isn't actually necessary, but on a long run and with insulation round them, they keep the gasses hot so they don't slow down as they reach the top of the chimney. This keeps a good draw. But without a liner, you'll get a bit of heat transferring to bedroom above. It is actually acceptable to just have a closure plate with an access hole in the chimney throat above the stove.
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